The present invention relates to printing devices. More particularly, the present invention relates to an apparatus and method for drying printing composition on a print medium.
Printing devices, such as inkjet printers and laser printers, use printing composition (e.g., ink or toner) to print images (text, graphics, etc.) onto a print medium in a printzone of the printing device. Inkjet printers may use print cartridges, also known as xe2x80x9cpensxe2x80x9d, which shoot drops of printing composition, referred to generally herein as xe2x80x9cinkxe2x80x9d, onto a print medium such as paper, transparency or cloth. Each pen has a printhead that includes a plurality of nozzles. Each nozzle has an orifice through which the drops are ejected. To print an image, the printhead is propelled back and forth across the page by, for example, a carriage while ejecting drops of ink in a desired pattern as the printhead moves. The particular ink ejection mechanism within the printhead may take on a variety of different forms known to those skilled in the art, such as thermal printhead technology. For thermal printheads, the ink may be a liquid, with dissolved colorants or pigments dispersed in a solvent.
In a current thermal system, a barrier layer containing ink channels and vaporization chambers is located between an orifice plate and a substrate layer. This substrate layer typically contains linear arrays of heating elements, such as resistors, which are energized to heat ink within the vaporization chambers. Upon heating, the ink in the vaporization chamber turns into a gaseous state and forces or ejects an ink drop from a orifice associated with the energized resistor. By selectively energizing the resistors as the printhead moves across the print medium, the ink is expelled in a pattern onto the print medium to form a desired image (e.g., picture, chart or text).
In order for the image to be fixed to the print medium so that it will not smear, the printing composition must be dried. The printing composition is dried by a combination of the solvent evaporating and the solvent absorbing into the print medium, both of which take time. Various factors control the amount of time required for a particular printing composition to dry. These factors include the type of print medium, the quantity of solvent in an printing composition, the amount of printing composition on the print medium, and ambient temperature and humidity. Ideally, the printing composition will be fixed to the print medium quickly to help prevent image smear, print medium cockle (print medium buckle toward a printhead), and print medium curl (curling along at least one edge of a print medium), as well as to help maximize printing device throughput.
To reduce the amount of this time, the surface of some types of print media may be specially coated to help speed drying. Other means may also be used such as special chemicals, generally know as xe2x80x9cfixersxe2x80x9d, that are applied to print media before or after printing. Pressure may also be applied, alone or in combination with heat from a heating device, to help reduce this amount of time. Various types of heating devices may also be used to heat print media before and/or after printing.
Each of these above-described techniques have certain disadvantages. For example, specially coated print media may be relatively more expensive than uncoated print media. Fixers may become depleted during printing, resulting in no fixer being applied for the remainder of a print job, possibly causing some or all of the aforementioned problems, or the stopping of a print job to supply additional fixer, resulting in decreased printing device throughput and possible color hue shift on the print medium for which printing was halted.
Pressure generating devices, such as pressure rollers, can cause image smear. Also, pressure generating devices add to the overall cost, size and complexity of the printing device.
Heating devices are often expensive to operate in those printing devices that produce large quantities of printed output. Another consequence of such high throughput printing devices that use heating devices to dry printing composition on print media is excess heat generation. If excessive, heat shielding or heat absorbing members inside the printing device may be necessary both to help protect various components of a printing device from such excess heat and to help dissipate such excess heat. Such extra components add to the overall cost, size, and complexity of the printing device.
An apparatus and method that decreased the amount of time required to dry or fix printing composition to a print medium while avoiding the above-described problems associated with other techniques would be a welcome improvement. Accordingly, the present invention is directed to drying or fixing printing composition to a print medium quickly to help prevent image smear, print media cockle, and print media curl. The present invention is also directed to helping maximize printing device throughput and minimize excessive heat generation so that the above-described wasted heat energy is avoided and heat shielding and heat absorbing members are unnecessary, thereby avoiding the above-described problems associated with such devices. The present invention is additionally directed to eliminating the need for pressure generating devices to help dry or fix printing composition to print media, thereby also avoiding the above-noted problems associated with such devices. The present invention is further directed to eliminating the need for specially coated media and fixers to accelerate drying.
Accordingly, an embodiment of a method in accordance with the present invention for use in a printing device includes depositing printing composition onto a print medium and enclosing the print medium in a sealed environment. The method additionally includes reducing a pressure in the sealed environment below an ambient pressure and heating the print medium in the sealed environment to dry the printing composition on the print medium.
The above-described embodiment of a method in accordance with the present invention may be modified and include the following characteristics, as described below. The method may further include raising the pressure in the sealed environment to the ambient pressure subsequent to heating. The method may also include capturing liquid removed from the printing composition during heating.
An embodiment of an apparatus in accordance with the present invention for use in a printing device having a print engine for depositing a printing composition onto a print medium includes structure for enclosing the print medium in a sealed environment. The apparatus additionally includes structure for reducing a pressure in the sealed environment below an ambient pressure and structure for heating the print medium in the sealed environment to dry the printing composition on the print medium.
The above-described embodiment of an apparatus in accordance with the present invention may be modified and include the following characteristics, as described below. The apparatus may also include structure for raising the pressure in the sealed environment to the ambient pressure subsequent to heating. The apparatus may also include structure for capturing liquid removed from the printing composition during heating.
An alternative embodiment of an apparatus in accordance with the present invention for use in a printing device having a print engine for depositing a printing composition onto a print medium includes an enclosure configured to provide a sealed environment around the print medium. The apparatus additionally includes a vacuum source fluidly coupled to the enclosure and configured to reduce a pressure in the sealed environment below an ambient pressure and a heater configured to apply heat energy to the print medium in the sealed environment to dry the printing composition on the print medium.
The above-described alternative embodiment of an apparatus in accordance with the present invention may be modified and include the following characteristics, as described below. The apparatus may also include a valve fluidly coupled to the enclosure and configured to raise a pressure in the sealed environment to the ambient pressure subsequent to heating. The apparatus may also include an accumulator for capturing liquid removed from the printing composition during heating.
The foregoing summary is not intended by the inventors to be an inclusive list of all the aspects, advantages, and features of the present invention, nor should any limitation on the scope of the invention be implied therefrom. This summary is provided in accordance with 37 C.F.R. Section 1.73 and M.P.E.P. Section 608.01(d). Other objects, advantages, and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.